H. Y. He

Electronic Structures and Raman Features of a Carbon Nanobud

By employing the first-principles calculations, we investigate electronic properties of a novel carbon nanostructure called a carbon nanobud, in which a

Theoretical prediction of new carbon allotropes

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The dynamical process of the phase transition from VO2(M) to VO2(R)

molecule covalently attaches or embeds in an armchair carbon nanotube. We find that the carbon nanobud exhibits either semiconducting or metallic behavior, depending on the size of the nanotube, as well as the combination mode. Moreover, with respect to the case of the corresponding pristine nanotubes, some new electronic states appear at 0.3-0.8 eV above the Fermi level for the carbon nanobuds with the attaching mode, which agrees well with the experimental reports. In addition, the vibrational properties of the carbon nanobuds are explored. The characteristic Raman active modes for both

An empirical law for the band gaps of MgZnO nanowires

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Origin of the Giant Negative Thermal Expansion in

and the corresponding pristine nanotube present in Raman spectra of the carbon nanobuds with attaching modes, consistent with the observations of a recent experiment. In contrast, such situation does not appear for the case of the carbon nanobud with the embedding mode. This indicates that the synthesized carbon nanobuds are probably of the attaching configuration rather than the embedding configuration.

The formation of H bubbles at small-angle tilt grain boundaries in W films.

Novel carbon allotropes are predicted by optionally substituting carbon atoms in diamond with carbon tetrahedrons. All these allotropes exhibit semiconducting properties, with bandgaps ranging from 3.2 to 4.7 eV. The calculated cohesive energy, mass density, and the bulk modulus are essentially related with the component of the tetrahedron units in these allotropes. In particular, we reveal the evolution of mechanical and electronic properties with the component of tetrahedrons for this family of crystalline carbon allotropes. This sheds a new light of tuning electronic and elastic properties of new allotropes by controlling the composition of carbon tetrahedrons. In addition, the calculated Raman spectra for these allotropes exhibit different features, and Raman characteristic modes for the tetrahedron units are addressed, which are available for identifying these allotropes in experiment.

Site preference and diffusion behaviors of H influenced by the implanted-He in 3C-β SiC

The dynamical process of the metal-insulator transition, from VO2(M) to VO2(R), is studied in the framework of the dynamics theory. It is found that the thermal exciting of the Raman-active Ag mode with frequency of 212.7 cm-1 in the VO2(M) lattice drives the compound to be the VO2(R) lattice. The intermediate structures during the phase transition are revealed, from which we find that when the distortion of the atomic network away from its initial network in the M phase exceeds 60%, the system becomes metallic. At the moment, the monoclinic symmetry of the crystal remains still, but more V ions are dimerized. This strongly suggests that the dimerization of the V ions in the compound plays a critical role in the transition from the M phase to the R phase.

Structural Features and Electronic Properties of MgO Nanosheets and Nanobelts

The practice of semiconducting nanowires in the photoelectronic nano-devices requires that the band gaps of the nanowires are controllable in the process of the synthesis, where the bandgap of a semiconducting nanowire is highly dependent on its chemical components and the structural parameters. In this work, by performing theoretical calculations at the level of the density functional theory, the band gaps of the MgxZn1-xO nanowires with different contents of Mg and different structural features are extensively studied. Through correlating the calculated band gaps to both the contents of Mg and the structural parameters, we find that the bandgap of a MgxZn1-xO nanowire can be expressed by an empirical formula. Our calculations indicate that this formula is valid for the ZnO nanowires, the alloy MgZnO nanowires, as well as the ZnO/MgxZn1-xO core-shell nanowires. We anticipate that this empirical formula can serve as a guidance for designing a MgZnO nanowire with the desired bandgap in its realistic applic...

Electronic Structures and Vibrational Properties of a Carbon Nanotube with Adsorption of Small Hydrocarbon Radicals

The giant negative thermal expansion in the Ge-doped antiperovskite Mn3CuN compound is theoretically studied by using the first principles calculations. We propose that such a negative thermal expansion property is essentially attributed to the magnetic phase transition, rather than to the lattice vibration of the Ge-doped compound. Furthermore, we found that the doped Ge atoms in the compound significantly enhance the antiferromagnetic couplings between the nearest neighboring Mn ions, which effectively stabilizes the magnetic ground states. In addition, the nature of the temperature-dependent changes in the volume of the Ge-doped compound was revealed.

Characteristic vibrational modes of a single vacancy in a zigzag carbon nanotube

The accumulation of H at the small-angle tilt grain boundary (GB) in the W(001) surface is investigated, on the basis of the first-principles calculations. By exploring the solution and diffusion behaviors of H at the GB, we find that the small-angle GB can capture the H atoms nearby, serving as a nucleation site of H bubbles. With the increasing number of trapped H atoms, the GB expands gradually, and the GBs can be unripped with an areal density of H up to 5.0 × 1015 H atoms per cm2, leading to the formation of H bubbles. Moreover, H2 molecules are observed, when the areal density of H atoms in GB is over 6.6 × 1015 atoms per cm2. According to our calculations, we propose a possible formation mechanism of H bubbles observed in the experiment, which is valuable for improving the service performance of W as a plasma-facing material in nuclear fusion reactors.